A so-called indirect AC power converting apparatus is generally used as typical main circuitry of an inverter. In the indirect AC power converting apparatus, AC is rectified and is converted into DC via a smoothing circuit, whereby an AC output is obtained by a voltage-source converter.
On the other hand, as a mode of directly obtaining an AC output from an AC voltage, there is known a direct AC power converting apparatus represented by a matrix converter. The direct AC power converting apparatus does not require a large capacitor for smoothing a voltage ripple due to commercial frequency or a reactor. Accordingly, a direct AC power converting apparatus is expected to be miniaturized, and in recent year, it has been drawing attention as the next generation of a power converting apparatus.
For example, Japanese Patent Application Laid-Open No. 2004-222337, Japanese Patent Application Laid-Open No. 2004-266972, Japanese Patent Application Laid-Open No. 2007-312589 and WO 2007/123118 disclose the technology of directly converting AC to AC without using a smoothing circuit in a DC link. In particular, in Japanese Patent Application Laid-Open No. 2007-312589 and WO 2007/123118, it is aimed to facilitate control of a converter and an inverter by determining the timing at which the converter performs commutation in accordance with the results of comparison between a carrier and three trapezoidal waves that have phases shifted from each other by 120 degrees.
Further, Japanese Patent Application Laid-Open No. 2007-295686 discloses the technology of employing a clamp circuit using a device required to have a small breakdown voltage, to thereby solve a problem of regenerative current in a direct AC power converting apparatus.
Note that Japanese Patent No. 3806872, Japanese Patent Application Laid-Open No. 05-56682 and Japanese Patent No. 2524771 are related to the present application. Japanese Patent No. 3806872 discloses the technology of reducing errors in estimating a rotating position of a motor by causing the current to be supplied to be large and have a lagging phase. Japanese Patent Application Laid-Open No. 05-56682 discloses the technology of handling instantaneous stop/reactivation of a power source in an indirect AC power converting circuit. Japanese Patent No. 2524771 describes power conversion using a diode bridge equivalent to a natural commutation mode of a converter.
Note that as the documents related to the present application, there are further given: Lixiang Wei and Thomas A. Lipo, “A Novel Matrix Converter Topology with Simple Commutation”, IEEE IAS 2001, Vol. 3, 2001, pp. 1749-1754 (hereinafter, referred to as “A Novel Matrix Converter Topology with Simple Commutation”); Rie Itoh and Isao Takahashi, “Decoupling Control of Input and Output Reactive Power of the Matrix Converter”, IEEJ Technical Meeting on Semiconductor Power Converter, SPC-01-121, 2001 (hereinafter, referred to as “A Novel Matrix Converter Topology with Simple Commutation”); Koji Kato and Jun-ichi Itoh, “Improvement of Waveform for a Boost type AC/DC/AC Direct Converter”, Year 2007 IEEJ National Convention 4-098, 2007, pp. 153 and 154; Koji Kato and Jun-ichi Itoh, “Improvement of Waveform for a Boost type AC/DC/AC Direct Converter Focused on Input Current” Year 2007 IEEJ Industry Applied Section Meeting 1-31, pp. 279-282; Takaharu Takeshita, Koji Toyama and Nobuyuki Matsui, “PWM Scheme for Current Source Three-Phase Inverters and Converters”, IEEJ Transactions on Industry Applications, Vol. 116, No. 1, 1996, pp. 106 and 107 (hereinafter, referred to as “PWM Scheme for Current Source Three-Phase Inverters and Converters”); and Siyoung Kim, Seung-Ki Sul, Thomas A. Lipo, “AC/AC Power Conversion Based on Matrix Converter Topology with Unidirectional Switches”, IEEE trans. on Industry Applications, Vol. 36, No. 1, 2000, pp. 139-145 (hereinafter, referred to as “AC/AC Power Conversion Based on Matrix Converter Topology with Unidirectional Switches”).